The invention relates to a hydraulic vehicle brake system with a wheel slip regulator device.
EP O 482 367 A1 has disclosed a hydraulic vehicle brake system whose wheel slip regulator device is disposed between a two-circuit master cylinder and wheel brakes of four vehicle wheels and, for braking operation by means of the master cylinder through the actuation of the brake pedal, has a so-called return feed pump in each brake circuit. The feed pump can produce high pressure, and has electrically controllable directional control valve devices associated with the wheel brakes, wherein by means of the directional control valve devices, each of the wheel brakes of wheels that are in danger of locking can be temporarily isolated from the master cylinder and can be connected to the associated return feed pump so that this return feed pump conveys hydraulic fluid away from the respective wheel brake and back into the master cylinder. The vehicle brake system is also updated to limit drive slip of drivable wheels to a favorable slip value range by means of automatic brake pressure generation in at least one wheel brake of its driven wheels. One of the return feed pumps is used as a means for generating high pressure for this, which is supplied at a partial or full level, depending on conditions, by means of at least one of the directional control valve devices to the at least one wheel brake to change the drive slip by compensating for the driving torque surplus. For this automatic braking operation, the vehicle brake system has another pump unit, which has a low pressure pump in the form of a gear pump that is essentially leakage flow free or has only a small amount of leakage flow, a pressure limiting valve in a first bypass line disposed between an outlet and an inlet of the gear pump, a throttle in a second bypass line connected parallel to the first bypass line, and a motor to drive the low pressure pump.
For example, the gear pump is equipped with an internal geared ring and can be purchased under the name of "Gerotor pump" at the W. H. Nichols Company. For the operation of the drive slip regulator, this low pressure pump, by means of a check valve, supplies the return feed pump with hydraulic fluid aspirated from a reservoir and is used, by means of another check valve, to apply the brake linings of at least one wheel brake to its brake disk or brake drum at the beginning of an operation of the drive slip regulator.
When bleeding the completely assembled hydraulic vehicle brake system before it is filled with hydraulic fluid, the throttle and the second bypass are used to evacuate a connecting line leading from the outlet of the low pressure pump and branches to the check valves mentioned and are then used to fill this connecting line with hydraulic fluid by means of the reservoir. As a result, when the vehicle brake system is first operated, the low pressure pump does not force air into the vehicle brake system, which can disadvantageously reduce the effectiveness of the brake system in a known manner. The disposition of the two bypasses, the pressure limiting valve, and the separately embodied throttle is expensive, takes up space, and increases the weight of the vehicle brake system.
DE 42 26 646 A1 discloses another hydraulic vehicle brake system with a wheel slip regulator device between a master cylinder and wheel brakes of vehicle wheels and with a pump unit that supplies return feed pumps of the wheel slip regulator device for automatic braking. In addition to regulating or limiting drive slip by means of individual wheel brakes, this vehicle brake system is also furnished to generate yawing moments and/or to generate or change lateral slip of vehicle wheels to automatically improve the driving behavior of a vehicle equipped in this manner to aid the driver up to the limit of what is physically possible when negotiating curves. For example, the pump unit is embodied in the manner disclosed in EP 0 482 367 A1. What differs is that in the example of DE 42 26 446 A1, the pump unit supplies both return feed pumps with hydraulic fluid for automatic braking so that all the vehicle wheels associated with both brake circuits can be automatically braked as a function of conditions and can be braked independently of one another. DE 42 26 446 A1 discloses different brake circuit embodiments and different associations of front wheel brakes and rear wheel brakes to the brake circuits.
A hydraulic vehicle brake system disclosed by DE 42 32 311 C1, U.S. Pat. No. 5,501,514, likewise has a master cylinder, a wheel slip regulator device, a pump unit, and wheel brakes and additionally has a cylinder device with a dividing piston, which device is connected between the master cylinder and the wheel slip regulator device in each brake circuit. The cylinder devices with their dividing pistons have the task of conducting the pressure produced by the pump unit into the wheel slip regulator device and also of preventing the penetration of surrounding air aspirated by the pump unit. Correspondingly, only the contents of the cylinder devices are displaced into the wheel slip regulator device. At the beginning of an automatic braking operation, a partial quantity of the displaced hydraulic fluid reaches at least one of the wheel brakes for application of the brake lining, and another partial quantity is supplied to the respective return feed pump for the generation of brake pressure. The pump unit likewise corresponds to a construction disclosed by DE 42 26 646 A1 that has the expensive pressure limiting valve. The cylinder devices with the dividing piston also make the hydraulic brake system more expensive.